In general, acrylic acid is produced through a two-stage oxidation process comprising a step of catalytic reaction of propylene with oxygen to acrolein and a step of catalytic reaction of acrolein with oxygen to acrylic acid.
In recent years, on the other hand, for the reason that there is a difference in price between propane and propylene or the two-stage oxidation of propylene requires complicated steps, the production of acrylic acid using propane as a starting material through a one-stage process has been studied. Many proposals have been made on the catalyst for use in such a process. Representative examples of proposed catalysts include [V, P, Te]-based catalyst [as disclosed in "Catalysis Today", 13, 679 (1992)], AgBiVMoO (as disclosed in JP-A-2-83348 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")), BiMo.sub.12 V.sub.5 Nb.sub.0.5 SbKO.sub.n (as disclosed in U.S. Pat. No. 5,198,580), [Mo, Te, V, Nb]-based catalyst (as disclosed in JP-A-6-279351), and [Mo, Sb, V, Nb]-based catalyst (as disclosed in JP-A-9-316023 and JP-A-10-137585).
Furthermore, JP-A-10-230164 discloses an improvement in the catalyst for the production of acrylic acid disclosed in the above cited JP-A-9-316023 and JP-A-10-137585, i.e., process for the production of [Mo, Sb, V, Nb]-based oxide catalyst involving a first step of reacting V.sup.+5 and Sb.sup.+3 at a temperature of 70.degree. C. or higher in the presence of Mo.sup.+6 in an aqueous medium and bubbling molecular oxygen or a gas containing molecular oxygen through the reaction solution during or after the reaction and a second step of mixing an Nb compound with the reaction mixture and then calcining the mixture.
However, the above proposed catalyst is disadvantageous in that the yield of acrylic acid as the desired product is insufficient or life of the catalyst itself is short. For example, the [Mo, Te, V, Nb]-based catalyst proposed in the above cited JP-A-6-279351 allows the production of acrylic acid in a high yield but is liable to evaporate Te, thereby causing deterioration of catalytic activity with the lapse of time. Further, the [Mo, Sb, V, Nb]-based catalyst disclosed in JP-A-9-316023 and JP-A-10-230164 still has further improvement in the yield of acrylic acid or the reproducibility of production of catalyst. Further, where those catalysts are used for fluidized bed reaction, it is required for the catalysts to exhibit excellent catalytic properties as well as excellent abrasion resistance. Those catalysts are still insufficient in this respect.